Decoupling Fe<sup>0</sup> Application and Bioaugmentation in Space and Time Enables Microbial Reductive Dechlorination of Trichloroethene to Ethene: Evidence from Soil Columns
Srivatsan Mohana Rangan, Shefali Rao, Aide Robles, Aatikah Mouti, Laurie LaPat-Polasko, Gregory V. Lowry, Rosa Krajmalnik‐Brown, Anca G. Delgado
Abstract
High Resolution Image Download MS PowerPoint Slide Fe 0 is a powerful chemical reductant with applications for remediation of chlorinated solvents, including tetrachloroethene and trichloroethene. Its utilization efficiency at contaminated sites is limited because most of the electrons from Fe 0 are channeled to the reduction of water to H 2 rather than to the reduction of the contaminants. Coupling Fe 0 with H 2 -utilizing organohalide-respiring bacteria (i.e., Dehalococcoides mccartyi ) could enhance trichloroethene conversion to ethene while maximizing Fe 0 utilization efficiency. Columns packed with aquifer materials have been used to assess the efficacy of a treatment combining in space and time Fe 0 and a D. mccartyi -containing culture (bioaugmentation). To date, most column studies documented only partial conversion of the solvents to chlorinated byproducts, calling into question the feasibility of Fe 0 to promote complete microbial reductive dechlorination. In this study, we decoupled the application of Fe 0 in space and time from the addition of organic substrates and D. mccartyi -containing cultures. We used a column containing soil and Fe 0 (at 15 g L –1 in porewater) and fed it with groundwater as a proxy for an upstream Fe 0 injection zone dominated by abiotic reactions and biostimulated/bioaugmented soil columns (Bio-columns) as proxies for downstream microbiological zones. Results showed that Bio-columns receiving reduced groundwater from the Fe 0 -column supported microbial reductive dechlorination, yielding up to 98% trichloroethene conversion to ethene. The microbial community in the Bio-columns established with Fe 0 -reduced groundwater also sustained trichloroethene reduction to ethene (up to 100%) when challenged with aerobic groundwater. This study supports a conceptual model where decoupling the application of Fe 0 and biostimulation/bioaugmentation in space and/or time could augment microbial trichloroethene reductive dechlorination, particularly under oxic conditions.